Overview
- Stiftung Warentest reviewed 25 vitamin D products and found many unsuitable, with only Rotbäckchen Vital Vitamin D Saft and GSE Vitamin D Bio-Tabletten recommended without restrictions.
- The German risk authority BfR advises a daily maximum of about 20 µg (800 IU) and warns that high single depot doses around 20,000 IU and chronic excess can harm kidneys and raise safety risks.
- Health agencies say most healthy adults do not benefit from winter supplementation, while infants, older adults, people with little sun exposure or darker skin, and certain patients may need testing and treatment.
- Clinicians highlight interactions with nutrients such as vitamin K2, magnesium and calcium and recommend individualized dosing and simple monopreparations over fixed combination products.
- Authorities note that 80–90% of vitamin D comes from sunlight and only 10–20% from diet, so deficiency should be confirmed with a 25(OH)D blood test before starting supplements.